A new soldier (not the Engineers) is stiff in manner (7)
I believe the answer is:
angular
'stiff in manner' is the definition.
'angular' can be an answer for 'stiff' (I've seen this before). I'm unsure of the 'in manner' bit.
'a new soldier not the engineers' is the wordplay.
I cannot quite understand how this works, but
'a' could be 'an' and 'an' is found in the answer.
The remaining letters 'gular' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'is' acts as a link.
Can you help me to learn more?
(Other definitions for angular that I've seen before include "Pointed" , "With jagged outline" , "Having sharp lines and corners" , "Thin and bony - with sharp corners" , "Having sharp edges or corners" .)